Various forms of suspension systems have been proposed and developed for bicycles. The most common form of fork suspension system for bicycles is similar to that used on motorcycles and comprises a pair of telescoping assemblies between which the front wheel is mounted. Each telescoping assembly comprises an outer tube, and inner tube which is free to move in and out of the outer tube and is cushioned in some manner, as by springs and/or a hydraulic system. Generally, the outer tubes are connected at the lower ends to the axle of the front wheel of the bicycle, and the upper ends of the inner tubes are connected together in a fashion similar to the usual upper end of a bicycle fork and extend into the head tube of the bicycle frame. A number of examples of suspension forks for bicycles are shown in the February 1991 issue of Mountain Bike Action, particularly beginning at page 32 thereof. Other bicycle suspension arrangements comprise a single telescoping assembly coupled between the front wheel fork and the head tube of the bicycle frame. In either form of suspension, bushings usually are provided between the telescoping tubes to reduce friction.
Riders have found that suspension front forks can benefit handling and improve control, and a front suspension helps the front wheel follow the ground. A front suspension system is desirable for absorbing bumps, and can enable the bicycle to handle better at higher speeds and be more controllable under rough conditions. Although the front suspension systems of many motorcycles provide these features for motorcycles, they are bulky and heavy, and the designs thereof are not readily adaptable to bicycle use.
Several prior art examples of front suspension systems for bicycles are shown in Horack U.S. Pat. No. 689,970 and Moulton U.S. Pat. No. 3,208,767. The Horack system provides a spring suspension, and includes a ball bearing system for allowing both an axial telescoping action and a rotary steering action. The Moulton patent discloses a spline-type spring suspension. Other suspension systems of interest are shown in Thoms U.S. Pat. No. 723,075, Hutchins U.S. Pat. No. 2,477,748, Ryan U.S. Pat. No. 3,301,575, Hornsby U.S. Pat. No. 3,459,441, Zenser U.S. Pat. No. 3,964,765, Hartman U.S. Pat. No. 4,815,763, British Specification U.S. Pat. No. 295316 of Nov. 1928, and Italian Patent No. 416,260 of Nov. 1946.
As is known to those skilled in the art, any form of system using anti-friction bushings and the like have undesirable static friction called "stiction." Because of this, suspension systems using such bushings tend to stick and then suddenly release or move, and the point at which they release gets higher with higher loads (e.g., a higher radial load caused by a braking load). The dual telescoping assembly presently used on some bicycles is essentially an adaptation of motorcycle front suspension technology; however, in addition to the weight and bulkyness problems, the two telescoping assemblies also have to be fixed together in some manner, as through a "U " shaped yoke at the upper ends of the tubes to eliminate the attendant twisting problem that occurs with each telescoping assembly. This generally is not a problem with motorcycles because the suspension fork assembly can be large and bulky so as to overcome this twisting problem. Additionally, there are linkage type systems, such as the aircraft landing gear scissors link, but this involves an additional coupling with its attendant weight, size and complexity.
It is desirable to provide a front suspension system or suspension fork for bicycles, and particularly for light weight bicycles, which can bear a combination of loads comprising very high radial loads (e.g., from front to back) occasioned by braking, bumps and the like, while at the same time providing stable and tight rotational motion in steering of the front wheel through the suspension system from the handlebars.